#include <iostream>
#include <vector>
using namespace std; 


class Solution {
    int m, n;
    bool vis[101][101] = { 0 };
    int dx[4] = {0, 0, 1, -1};
    int dy[4] = {1, -1, 0, 0};
  public:
    bool exist(vector<string>& board, string word) {
        m = board.size(), n = board[0].size();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (board[i][j] == word[0]) {
                    if (dfs(board, i, j, word, 0)) return true;
                }
            }
        }
        return false;
    }
    bool dfs(vector<string>& board, int i, int j, string& word, int pos) {
        if (pos == word.size() - 1) {
            return true;
        }
        vis[i][j] = true;
        for (int k = 0; k < 4; k++) {
            int a = i + dx[k], b = j + dy[k];
            if (a >= 0 && a < m && b >= 0 && b < n && !vis[a][b] && board[a][b]
                    == word[pos + 1]) {
                if (dfs(board, a, b, word, pos + 1)) return true;
            }
        }
        vis[i][j] = false;
        return false;
    }
};